1. Field of the Invention
The present invention relates generally to purge or bubble tube type devices used for the measurement of the depth of a quantity of liquid. More specifically, the present invention is directed to a system using such a purge type apparatus for precisely measuring both the pressure head and the properties of the liquid at the bubble tube outlet by means of the “bubble signature,” which varies due to the properties of the liquid.
2. Description of the Related Art
The purge or bubble tube principle of determining the depth of a quantity of liquid is well known. The present inventor has a previously issued (U.S. Pat. No. 6,510,736, discussed further below in greater detail) which discloses various improvements in such devices. Such purge type systems can provide various advantages in the accuracy and response times of liquid depth or level indicator systems, and are used in various different environments for rapidly and accurately filling containers in the bottling and other industries.
However, in many instances it is not only important to be able to accurately measure the quantity of a liquid, but also to be able to test the liquid for impurities or adulteration by another liquid of some other type. One field in which this is extremely critical is aviation. Water is an occasional contaminant of aviation fuels (both gasoline and turbine fuels) and its incombustibility can result in disaster if a significant quantity of water is ingested by the aircraft engine. Yet, aircraft fuel systems are quite prone to water contamination, as most aircraft spend most of their lives outside where precipitation can flow into lower areas around recessed fuel caps and thence into the fuel tanks if the caps seal less than perfectly. Water is also occasionally pumped into aircraft fuel tanks due to contamination of the fuel supply. A perhaps even more common means for water to contaminate fuel systems is through condensation in a partially filled fuel tank. Moisture will often condense on the sides of the tank and run to the bottom of the tank, due to the density of the water being greater than that of the fuel in the tank. Since the fuel pickup in a fuel tank is always at or adjacent the lowest point in the tank in order to draw all (or nearly all) of the fuel from the tank, the fuel system will draw water from the tank if there is any significant amount within the tank. As a result, it is common practice to drain a sample of fuel from each tank and low point in an aircraft before flight, in order to check for contamination of the fuel supply. Essentially the same problems can occur in fuel oil tanks used for home heating, as well as other motor vehicle tanks. The use of alcohol additives in automobile fuel tanks to dissolve ice which has frozen in the fuel lines is well known in northern climes in the winter.
However, fuel contamination can also occur due to other factors. Another example from the aviation field is the contamination of one type of fuel, e.g. aviation gasoline, with another type, e.g. jet turbine fuel. While turbine engines can run reasonably well on fuels having a relatively high percentage of gasoline mixed therewith, the reverse is not true. Any significant quantity of turbine fuel, with its relatively low octane, will lead to detonation and engine damage in a spark ignition reciprocating engine. Although great care is universally used in refueling aircraft with the proper fuel, there have been accidents in the past from time to time in which turbine fuel has been used to refuel a reciprocating engine powered aircraft.
While there are various tests available for checking the type of fuel in a tank or container, and/or checking fuel for contamination, most such means are not an integral part of the fuel system of the aircraft or other system. Rather, such tests must be carried out on the ground, generally at some specialized test site or location. Such tests do nothing to measure or determine the quantity of fuel in the tank or container, in any event.
Accordingly, what is needed is a small, inexpensive apparatus which may be integrated with a fuel or other liquid container system, which apparatus may serve to both measure the pressure head of the liquid within the container, and also to check the liquid for contamination by another liquid in the lower portion of the tank. The present invention provides such a device in the form of a purge or bubble tube type system, which serves to accurately measure the pressure head (and thus the quantity, if the tank configuration is known) of the liquid within the container or tank, and which also may be used to Distinguish between different types of liquids at the outlet of the bubble tube due to the different “bubble signatures” which result as the bubble stream enters different liquids having different surface tensions and other properties from one another.
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 3,729,997 issued on May 1, 1973 to Owen B. Luke, titled “Liquid Level Sensor,” describes a mechanical diaphragm type pressure regulator for controlling the pressure output to a bubble tube. The device essentially serves as a gas pressure control device required of any purge type system, but no specific means is disclosed by Luke to provide the required gas pressure or to measure the liquid depth or head by means of the pressure. In any event, the relatively simple mechanical device of the Luke U.S. Patent is incapable of determining differences in the bubble or pressure signature of the purge system while it is in operation, and thus cannot distinguish between different liquids, as can the present invention.
U.S. Pat. No. 3,987,675 issued on Oct. 26, 1976 to Christopher R. Harrison, titled “Pneumatic Level Sensing,” describes a system for use with relatively large and deep tanks, as in ocean going tanker ships. Harrison requires a series of dip tubes which penetrate the tank, i.e. lower and upper bubble tubes and a balance tube, each of which increases the chance of leakage at the point of penetration. The present system requires only a single point of penetration into a closed tank. Moreover, the Harrison system requires a relatively high pressure head due to the depth of the liquid in such large tanks, and cannot make use of the relatively small pressure pump of the present invention, with its extremely high accuracy and resolution. Also, while Harrison describes a means of determining the density of the fluid in the tank by means of the difference in pressure in the down tubes, his system only works when the tank is completely full, i.e. the higher tube detects the presence of liquid to indicate the level of the liquid in the tank. Otherwise, the Harrison system cannot simultaneously determine both the level and the density of the liquid in the tank. The present invention provides a means of simultaneously determining both the pressure head or depth of the liquid in the tank, as well as the properties of the liquid at the lower end of the bubble tube by means of the bubble signature provided.
U.S. Pat. No. 4,297,081 issued on Oct. 27, 1981 to William A. Irvin, titled “Liquid Level Control System,” describes a purge type system using a multiple electrical contact mercury manometer type switch. The pneumatic pump for the bubble tube is also connected in parallel to the mercury manometer, with higher pressures due to greater liquid depth resulting in higher mercury levels in the manometer. The manometer contains only a finite number of switches therein, and thus the device cannot provide indications of infinitesimally small increments, as can the present depth indicator system. Moreover, Irvin does not disclose any means of using a small and highly accurate pneumatic pump to operate his system, and to provide distinctive bubble signatures which may be resolved to determine the type of liquid disposed at the outlet of the bubble tube, as provided by the present invention.
U.S. Pat. No. 4,984,451 issued on Jan. 15, 1991 to Don J. Wilen et al., titled “Method For Determining Physical Properties Of Liquids,” describes a system in which two dip tubes and a temperature probe are inserted into a container of liquid and used to determine the density or specific gravity of the liquid. The system operates using the same general principle as that described in the Harrison '675 U.S. Patent described further above, but on a much smaller scale and with greater precision. The Wilen et al. apparatus includes means to stop the gas flow in order to stabilize the pneumatic pressure upon release of gas bubbles from the lower ends of the two dip tubes, in order to allow the pressures to stabilize to provide an extremely accurate reading. By knowing the precise difference in height of the ends of the two dip tubes, the specific gravity of the liquid may be calculated with extreme accuracy. However, Wilen et al. teach away from the use of the bubble signature produced by continuous flow from the dip tube, to provide additional information. Wilen et al. treat this continuous variation in pressure as “noise” (column 1, line 49). The present invention analyzes this pressure variation during continuous flow to provide a “bubble signature,” which is used to determine various characteristics, and thus the liquid type, at the lower end of the dip tube.
U.S. Pat. No. 5,059,954 issued on Oct. 22, 1991 to Paul M. Beldham et al., titled “Liquid Level Sensing System,” describes a bubble tube or purge type system having intermittent operation and a timer delay in the system. When pressure falls below a predetermined level, the pneumatic pump is actuated to raise the pressure. The timer delay is also actuated. If pressure increases before the time delay period expires, this indicates that there is a leak in the pneumatic system, rather than the cause of the low pressure being a low liquid level. Otherwise, an alarm is actuated to indicate a low liquid level and the need to replenish the liquid quantity. The Beldham et al. system discloses only an open container or tank configuration, with no concentric vent system for use with closed containers, as provided in at least one embodiment of the present invention. Moreover, Beldham et al. do not disclose any means of analyzing the bubble signature from their system to determine the physical characteristics of the liquid at the lower end of the dip tube.
U.S. Pat. No. 5,163,324 issued on Nov. 17, 1992 to Glen A. Stewart, titled “Bubbler Liquid Level Sensing System,” describes a system similar to that of the Harrison '675 U.S. Patent described further above, in that Stewart provides a high and a low dip tube in a closed tank. However, Stewart connects the two tubes to two separate valves and thence to a single transducer. Stewart also provides for venting the fuel vapors to the atmosphere from the transducer lines, in order to reduce the chance of damage to the transducer due to fuel vapors. The Stewart system is thus not usable in automobiles sold in the United States, as fuel vapors must be contained in such vehicles due to emissions laws. The present invention avoids any such venting of vapors to the atmosphere, and preferably provides for the upper and lower tubes to be concentric in the tank with only a single entry point in order to reduce the chance of leakage in the tank.
U.S. Pat. No. 5,953,954 issued on Sep. 21, 1999 to François Drain et al., titled “Installation And Method For Determining The Level And Density Of A Liquid In A Tank, Using A Single Immersed Bubble Probe,” describes a purge type system in which the lower portion of the single tube has a larger diameter than the upper portion. Pressure is periodically reduced to zero relative to ambient tank pressure, allowing the liquid to rise within the tube to the level within the remainder of the tank. When pressure is applied to the tube, the pressure rise within the relatively smaller diameter portion of the tube is relatively rapid, and rises more slowly as the liquid is forced from the larger diameter lower portion of the tube. Knowing the height of the larger diameter portion of the tube (as well as the height of the mouth of the tube from the bottom of the tank), both the density and pressure head of the liquid may be calculated. Drain also discloses means for detecting contamination buildup within the tube, or around its mouth, by means of the uneven pressure rise as the tube is filled with air. However, he does not describe any means for detecting and measuring the bubble signature as the bubble(s) is/are released from the bottom of the tube, and correlating such signatures with the properties of the liquid at the lower end of the tube to determine the type of liquid at the mouth of the tube, as is done with the present invention.
U.S. Pat. No. 6,510,736 issued on Jan. 28, 2003 to William J. Van Ee, titled “Liquid Depth Sensing System,” describes various embodiments of a purge type pneumatic depth sensing system and electrical circuitry therefor. Each of the embodiments includes separate purge or bubble tubes and vent tubes, with closed tank embodiments including a third tube for drawing gas from the tank for recirculation in a closed system. The present inventor is also the inventor of the devices of the '736 U.S. Patent. The present invention improves upon this system by providing concentric bubble and vent tubes in a single passage through the top of the tank, thereby reducing the chance of leakage. Moreover, the present system may include temperature probes to provide some of the information required to determine the type of liquid at the outlet of the bubble tube, in accordance with the viscosity and surface tension of the liquid according to the bubble signature developed. The present system also differs from the Van Ee '736 U.S. Patent in that the present system utilizes a piezoelectric pump, rather than requiring a separate motor or solenoid to drive the pump, as in the '736 U.S. Patent disclosure.
U.S. Pat. No. 6,513,376 issued on Feb. 4, 2003 to Zachary A. Prather et al., titled “Liquid Level Height Measurement System,” describes a purge or bubble tube system for determining the depth of a liquid in a container, which also uses the gas which is passed through the bubble tube to carry titanium vapor for depositing upon integrated circuit boards. The system includes a series of pressurized gas containers which may be selected to supply different gases as desired. As the containers are pressurized, no pump is required in the Prather et al. system. Prather et al. do not disclose any means for measuring the minute pressure changes as gas bubbles pass from the end of the tube, and using these pressure changes to determine the type of liquid disposed at the outlet end of the tube, as provided by the present invention.
U.S. Pat. No. 6,539,796 issued on Apr. 1, 2003 to Yoshikatsu Shirai et al., titled “Liquid Level Sensor, Ampoule, And Liquid Amount Detection Method,” describes a system which primary purpose is to entrain vapors from a closed tank and deposit the vapors on integrated chips to form microelectronic circuitry. The Shirai et al. system uses compressed helium as the gas, with the helium also being used in a purge tube liquid quantity measuring system, similar to the system of the Prather '376 U.S. Patent discussed immediately above. Shirai et al. have no motivation to detect foreign liquids in their system, as the system is completely closed with no possibility of contaminants entering the system.
U.S. Pat. No. 6,647,781 issued on Nov. 18, 2003 to Tyan Khak Su, titled “Bubble Water Depth Measuring Method And System Thereof,” describes a system including a series of temperature compensated manometers along with a purge or bubble tube. The Su system is of relatively large scale and is adapted for measuring the depth of a relatively deep body of water, such as a lake. Su requires the temperature compensated manometers to correct for the different temperatures often found at different depths in relatively deep bodies of water. As the Su device is adapted for deep bodies of water, a relatively high pressure air pump is required to produce the pressures required to at least slightly exceed the pressures a the bottom of the body of water. A piezoelectric pump, as used in the present invention, is insufficient for use with the Su device.
Japanese Patent Publication No. 59-73,732 published on Apr. 26, 1984, titled “Purge Type Liquid Level Gauge,” describes (according to the drawings an English abstract) a purge type depth indication system including periodic high pressure purges of the dip tube to flush any buildup from the tip of the tube. This system teaches away from the present system, as the system must use a relatively high pressure pump in order to provide the required pressure for flushing the tube. The small, low pressure piezoelectric pump used with the system of the present invention is not suited for use with the Hirayama device. Moreover, the patent does not disclose any means to analyze the bubble signature of his system, in order to determine the properties of the liquid at the lower end of the tube.
Japanese Patent Publication No. 60-88,324 published on May 18, 1985, titled “Purge Type Level Gauge,” describes (according to the drawings and English abstract) an insert placed in the outlet end of the tube, to prevent droplet backsplash up the tube when a bubble is released. This prevents condensate buildup and corresponding restriction of the end of the bubble tube. The patent does not disclose any specific type of pneumatic pump, nor any means of analyzing the bubble signature to determine the properties of the liquid at the outlet end of the tube, as provided by the present system.
Japanese Patent Publication No. 60-102,524 published on Jun. 6, 1985, titled “Liquid-Level Measuring Apparatus,” describes (according to the drawings and English abstract) a system which detects leaks in the pneumatic components by means of a frequency detector. The system correlates the bubble rate with the frequency of the alternating signal generated by the bubble stream. The system utilizes a series of separate tubes and lines into the tank, rather than a single entry point with concentric lines, as in the present invention. Moreover, no disclosure is made of analyzing the bubble signature to determine the type of liquid at the outlet end of the tube, as provided by the present invention. The system considers only the overall pulse frequency of the bubbles to detect leaks in the system, with no disclosure being apparent as to the recognition of how the shape of the pulse corresponds to the viscosity and surface tension of the liquid at the lower end of the tube, as recognized by the present invention.
Japanese Patent Publication No. 63-191,026 published on Aug. 8, 1988, titled “Purge Type Liquid Level Indicator,” describes (according to the drawings and English abstract) a system for detecting condensate buildup in the output end of the bubble tube of such an apparatus. The apparatus of the '026 Japanese Patent Publication utilizes a microphone at the outlet end of the bubble tube. The sound is transformed to an electrical signal and compared to a reference signal. If the microphone signal varies beyond a predetermined level from the reference signal, an alarm is actuated to indicate the need to clean the tube. The present invention utilizes a completely different principle of signal detection and analysis for a different purpose. The present invention considers the electrical signal produced as pressure changes during the bubble release cycle, and considers the actions of the properties of various liquids upon the bubble release and resulting electrical signal to determine the type of liquid disposed at the outlet end of the tube, i.e. at the bubble release point. The '026 system does not anticipate such a possibility in any of his patent publications.
Japanese Patent Publication No. 1-74,420 published on Mar. 20, 1989, titled “Liquid Level Measuring Instrument,” describes (according to the drawings and English abstract) a system closely related to the system of the '796 U.S. Patent to Shirai et al., in that it describes a single pressurized gas cylinder connected to a series of purge tubes in a series of separate tanks. No pump means is disclosed, as none is necessary due to the pressurized gas source.
German Patent Publication No. 19,826,487 published on Dec. 16, 1999, titled “Filling Level Measuring System For Measuring Level Position Of Liquid In Container According To Hydrostatic Principle With Pipeline Immersed In Liquid Which By Means Of Pump,” describes (according to the drawings and English abstract) the computerized analysis of the pressure curve of the bubble stream in a purge type depth indicating system. The system averages out the pressure variations of the individual bubble pulses, and compares the pressure to a predetermined pressure to indicate when the container has been filled. The Spindler system is more closely related to the Wilen et al. '451 U.S. Patent with its averaging of the bubble signature, than it is to the present invention with its analysis of the individual pressure variations of the bubble release in order to determine the properties of the liquid at the lower end of the dip tube.
Finally, a web page published by SITA Messtechnik Gmbh, at least as of Mar. 16, 2004, describes the principles of the phenomenon of surface tension, and a series of instruments and programs for measuring the surface tension of a liquid by measuring the duration of the bubbles produced in a purge tube apparatus. The various instruments and programs are primarily directed to analyzing the concentration of surfactants (detergents) in water, for use in the commercial laundry industry. However, these instruments and surface tension measurement systems teach away from the present invention, as they are only directed to the results of the addition of a single substance, i.e. a detergent or surfactant, to water. No consideration is shown for the effects of other types of liquids on the bubble frequency, nor is the effect of different liquid viscosities considered. In contrast, the present invention considers the overall bubble signature, i.e. pressure changes and duration, to arrive at a signal which is unique for different liquids. In this manner, the contamination of one liquid in a container by another liquid disposed at the bottom of the container can be detected using the present system.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a liquid depth sensing system with liquid identification capability solving the aforementioned problems is desired.